MLGW replacing dangerous iron gas lines in $100 million-plus project

May 6, 2016 — Memphis Light, Gas & Water crew members Jabari Johnson (right) and Irvin Jackson (left) dig a hole on Walker near Wellington as they prepare to replacing old cast-iron gas lines dating back to the 1930s. The city will replacing the cast-iron pipes with safer high-pressure polyethylene lines as a part of a 30-year, $100 million-plus program. (Mark Weber/The Commercial Appeal)(Photo: Mark Weber)

On a sun-drenched street in South Memphis, a five-man utility crew last week dug through the pavement with backhoes and shovels in search of gas — or, more specifically, the network of aging natural gas pipes making up one of the most potentially dangerous components of the city's infrastructure.

Cast-iron mains, some dating to the 1930s, carry natural gas to customers in parts of Memphis within the Interstate-40-240 loop. Corrosive and brittle, they're prone to leaks and highly vulnerable to earthquakes emanating from the New Madrid Fault Zone.

As part of a $100 million-plus initiative spanning three decades, the Memphis Light, Gas and Water Division has been methodically replacing the cast-iron pipes with smaller, safer and more efficient polyethylene lines. The effort began in the early 1990s, following an agreement between the utility and the Tennessee Regulatory Authority, and isn't slated for completion until the end of 2021.

But MLGW has made substantial progress in the project. Of the 330 miles of cast-iron pipes originally in the system, all but 35-40 miles have been replaced with polyethylene.

The network of cast-iron main has reached the end of its 'shelf life,' said Craig Powers, manager of construction and maintenance for MLGW's gas division. 'Now it's basically part of the aging infrastructure that we're looking to replace.'

The potential dangers of cast-iron pipes were underscored in a March 2014 natural gas explosion that leveled two buildings in East Harlem, in New York City, killing eight people and injuring at least 50 others. The block had been served by a leaky 127-year-old cast-iron main.

A spate of similar incidents prompted the Pipeline & Hazardous Materials Safety Administration, which is part of the federal Department of Transportation, to issue a 'call to action' in 2011 to accelerate the repair and replacement of dangerous pipeline facilities.

Only about 3 percent of the 2.1 million miles of gas distribution and service lines in the U.S. are made of cast or wrought iron, according to the PHMSA. But most of those lines are in major cities, where cracks and leaks caused by freezing and thawing could endanger more lives.

MLGW figures show the gradual replacement project already is improving safety. The number of cast-iron leaks in the system dropped from 49 in 2014 to 22 last year.

'What we wanted to do was reduce natural gas incidents,' Powers said.

But safety isn't the only reason for the switch. Because they can accommodate greater pressure, polyethylene lines also are smaller in diameter, requiring less space beneath the city's streets.

As his crew dug beneath Walker Avenue between Wellington and Mississippi in South Memphis, foreman Sid Riley said the 2-inch polyethylene line that will be installed will have a capacity of about 150 pounds of pressure per square inch. The 6-inch cast iron main it is replacing can handle only 30 pounds per square inch.

The utility has been budgeting about $4.5 million a year, on average, to pay for the ambitious replacement effort. But other than torn-up pavement on scattered streets, 'the customers won't notice anything,' Powers said.

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